This invention relates to discharge lamp units, and more particularly to a discharge lamp unit which has discharge electrodes confronted with each other in a closed glass tube.
A conventional discharge lamp unit of this type is constructed as shown in FIG. 1. A pair of lead supports 3 and 4 serving as conductors are embedded in an insulating base 2, which is a lamp holder of molded of a synthetic resin. The lead supports 3 and 4 support a discharge lamp 5. In the discharge lamp 5, a pair of electrodes 6 are held confronted with each other in a closed glass tube 5a. The closed glass tube 5a has pinch-sealed portions 5b at both ends, in which molybdenum foils 7 are sealed. The molybdenum foils 7 are connected to respective lead wires 8, which extend from the pinch-sealed portions 5b. Metal supports 9a and 9b are welded to the lead supports 3 and 4. At the rear end of the discharge lamp, the lead wire 8 is welded to the metal support 9a, and at the front end, the pinch-sealed portion 5b of the discharge lamp is held with the metal support 9b.
In the above-described conventional discharge lamp unit, the pinch-sealed portion 5b of the discharge lamp 5 because held by the metal support 9b is rectangular in cross section, as shown in FIG. 5, stress tends to concentrate at the corners thereof. In addition, stress applied to the pinch-sealed portion 5b during the pinch-sealing operation remains as initial stress (residual stress), so that the internal stress created in the pinch-sealed portion 5b when the latter is held by the metal support 9b is accordingly increased, as a result of which the pinch-sealed portion is liable crack at the corners. That is, the pinch-sealed portion suffers from a difficulty that it is low in durability.
The metal support 9b is bent in conformance with the configuration of the rectangular-section pinch-sealed portion 5b, which is considerably small. It is rather difficult to form the metal support 9b by bending a metal plate in this manner. Hence, the metal support 9b so formed is liable to be erroneous in its dimensions; that is, sometimes the holding portion of the metal support 9b is too loose or too tight.
Since the metal support 9b and the pinch-sealed portion 5b are both rectangular in section, they cannot be turned relative to each other, and it is accordingly difficult to adjust the position of the discharge region of the discharge lamp with respect to the reflector.